Flux for lead burning and method of making same



May 13, 1952 J. H. BOWDEN 2,596,466

FLUX FOR LEAD BURNING AND METHOD OF MAKING SAME Filed March 15, 1948 8 3 FIG Sn, Ag,Pb,Au Halide s Wv e NH -Holide Mol Percent 4 F G 7 Mol Percent Temperature 3 8 2 VVQNAA/ 9 ./vvww .0

FIG. 2

i Fluid Stage Semi Viscous Stage Vlseous Stage I Crystallization Point Super Cooled Liquid 5 v I l I l l l l I .4 8 l2 I6 20 24 2e 32 36 40 Time in Minutes INVENTOR.

Patented May 13, 1952 FLUX FOR LEAD BURNING AND METHQD OF MAKING SAME James H. Bowden, Chicago, Ill., assignor to National Cylinder Gas Company, Chicago, 111., a

corporation of Delaware Application March 15, 1948, Serial No. 14,932

6 Claims. 1

This invention relates to an improved flux for lead burning or the like, and it resides specifically in a novel composition which greatly facilitates the fusion-bonding of lead or alloys rich in lead to a variety of other metals.

Many circumstances make it necessary or desirable that lead or its alloys be bonded to other metals or to lead stru tures. This may be done for the purpose of utilizing the chemical properties of lead, for examnle, its resistance to acids, or it may be desired to take ad antage of such physical pro erties of lead as its density, malleability, ductility, or for other reasons. Many methods have been proposed for effe"ting the union of lead or its alloys to other metallic structures. A common expedient for this purpose is the practice kno n as lead burning and it is to the fusion-bonding technioues generally comprehended within this term that this invention is especially directed, althou h it is ap licable to other fusion-bonding methods. A description of the usual practice known as lead burning will be found in the art cle by Robert L. Ziegfeld appearing at pa es 34 to 37 of the Journal of the American Welding Society, V01..11. No. 9, September, 1932. For convenience, the term lead will be generally used herein to indicate the pure metal. its ordinary commercial forms, as well as alloys ri h in lead.

Lead burning ordinarily proceeds through the 3 application of a high degree of locali ed heat to the point of the union desired, while supplying lead to the same point where it is fused, and distributed in mo ten form as de ired. Ordinarily it is im ossible to obtain sufficient cohesion of lead eit er to lead structures or to other metals without employing special treatments to remove surface im urit es or metallic oxides from the site of the union desired. Fl xes are usually emp o ed to promote the cohesion of the lead to solid metal surfaces, and the flux material is considered to act by cleansing the surfaces and enabling them to be wetted by molten lead so that cohesion between the deposited lead and the surrounding surfaces is obtained. Zinc chloride and com ounds and mixtures derived from or including zinc chloride are the best known fiuxing agents, although many other substances and mixtures have been proposed for the purpose and have been used with varying degrees of success.

My invention provides a flux which, although it may be based on zinc chloride as a preferred ingredient, makes possible a heretofore unobtainableease of operation in lead burning procedures, and allows the omission of many operations formerly found to be essential in securing adequate union between lead and metal structures. The advantages and improvements in the art of lead burning made possible by this novel flux and the objects attained by my invention will be apparent from the description taken in conjunction with the drawing in which:

Fig. 1 is a ternary diagram graphically presenting relationships between molecular proportions of certain constituents of my new flux composition; and

Fig. 2 is a curve depicting the behavior on cooling (or melting) of a typical flux composition embodying my invention.

The process industries commonly employ lead as a lining for vessels made of iron or steel to enable these to withstand the action of acids and acid-reacting substances, such as dilute sulfuric acid and solutions of certain sulfate salts. Similarly, heating or cooling coils of copper and brass, or vessels formed of these metals, are frequently provided with a coating of lead to afford protection against the corrosive effects of various chemicals. The formation of such lined or coated structures is customarily accomolished by lead burning operations, since dip-coating or other coating methods usually will not provide the thickness of lead desired in the composite structure.

The formation of lead-lined steel tanks for sulfuric acid is typical of many such operations as heretofore practiced in this art. The steel surface to be coated is first cleaned to remove oxides, scale or the like, after which it is completely tinned with metallic tin, or with a tinlead solder, or a similar alloy. This is done to provide a surface to which lead can be bonded, although the presence of tin in the surface of the composite structure ultimately formed is undesirable. The tinned surface next is coated with substantially pure lead by the usual lead burning operation, and this lead coating is carefully cleaned, scra ed, and again coated with one or'more separately applied layers of lead. In the first of these o erations a flux is used, and the surface is carefully cleaned by wiping, scraping, or by like means, before the successive coatings are applied. The presence of tin in the coating initially applied is the primary reason for the application of successive and separate lead coatings, because tin has a marked tendency to migrate through the lead, and even a minute amount of tin in a lead surface in contact with acid results in rapid deterioration of the surface accompanied by the appearance of numerous pin holes through the lead coating.

My new flux makes possible the omission of the initial tinning step and permits decided simplification of the entire procedure. Through its use, a single coating of lead may be applied to steel surfaces and the lead is rapidly and firmly bonded thereto. No special preparation of steel surfaces is required, and, if more than one layer or coating of lead is desired, no elaborate cleaning methods between successive coats are necessary. Such simple and economical cleaning methods as sand blasting are adequate preparation for the bonding of lead to metal surfaces using the flux of this invention. Similar and equally important economies are possible in bonding lead to copper or brass structures; in applying coatings of lead by other methods, such as by dip-coating; and in wiping lead or solder onto metal structures prior to finishing or refinishing them for the purpose of filling minor surface imperfections to enable the production of a smoothly finished article.

The flux of this invention can be used with any source of heat in the same way that other fluxes are used, for example, with soldering irons and like sources of indirectly applied heat, but it has its greatest advantage when used with an open oxy-hydrogen flame, which is the normal tool of the lead burner.

The flux in which this invention resides is essentially composed of a halide of zinc or of cadmium, together with a minor amount of one or more of the halides of tin, silver, lead or gold, reacted with ammonia and containing a further small amount of one or more ammonium halides. Ammonium acid fluoride (NI-14F. HF) may be additionally included in the composition and it may, in part, replace one of the other ammonium halides. This is particularly advantageous when the flux is used to apply lead to surfaces which have been prepared by sand blasting, since the ammonium acid fiuoride is active to cleanse the surface of any minute amounts of silica or other silicious material. The ammonia with which the metal chlorides are reacted may be supplied as aqueous ammonium hydroxide or as gaseous ammonia. The amount of ammonia used is less than that required for complete formation of ammine complex salts with the metal halides, and, as will appear from the tables herein, the quantity should be at least about one-third and need not be more than about one-half of the theoretical amount. The reaction between the metal halides and the ammonia is exothermic, and proceeds with the evelution of considerable heat. Following completion of the reaction, and when the resulting flux has cooled somewhat, water may be added to the composition to control its consistency. If no water is used, the fiux is a hard, brittle mass and is difficult to apply. If a small amount of water is added, for example, about one-tenth of the total weight of the flux, the resulting products are at an elevated temperature, since its presence apparently causes hydrolysis of some of the metal compounds with a resultant loss of fiuxing properties in the product. The

to cleanse surfaces of silica or the like.

fiux of this invention after use leaves a residue which is substantially inert both to materials susceptible to corrosion by acids (steel and the like), and to metals susceptible to corrosion by alkaline substances (brass, copper and the like). When the flux is to be used to join lead to surfaces contaminated by small amounts of oil or grease, Water in the composition maybe replaced by isopropyl alcohol to achieve the consistency desired and to impart a degreasing action to the composition.

In general, the constituents of the fiux may be combined in molecular proportions as indicated by the following table: 7

Table 1- Zinc, or cadmium halides-. Tin, silver, lead or gold hal- 50 to mol percent ides 1 to l mol percent Ammonium halides 2 to 6 mol percent Ammonia (as III-E) 20 to 30 mol percent Water As desired;

Table 2 Zinc or cadmium halides 55 to 70mol percent Tin, silver, lead or gold halides 2 to 311101 percent Ammonium halides 3 to 6 molpercent Ammonia (as NI-hOI-l) l 20 to 30 mol percent Water As desired.

In the flux compositions, ammonium acid fluoride may partially replace the other ammonium halides and may be present up to a maximum of about 3 mol percent.

Fig. 1 'of the drawing illustrates the relationships of themolecular proportions of the first three constituents of Tables l and 2. The area bonded by the larger of the two polygons FGI-IIJF generally defines the limits of the most useful compositions of this invention corresponding to those of Table 1, while the area enclosed by the smaller parallelogram BCDEB shows a generally preferable group of fluxes corresponding to those of Table 2. In the (use gram of Fig. l and in the tables, the ammonium halides referred to are those other than such amounts of ammonium acid fluoride as are in? cluded for the special purpose of providing the fluxes with a cleansing action for silica.

Preferred flux compositions are derived from zinc halides, in particular, zinc chloride, with halides of tin and silver, preferably mixtures of stannous chloride and silver chloride in which the former is present in greater amount than the latter. Cadmium halides can rep-lace the zinc salts in the flux of my invention, but fluxes made from the cadmium salts are less desirable both from the standpoints of fluxing qualities and economy than are those containing zinc salts. If iodides are used, a characteristic coloration appears on the metal surfaces in contact with the heated flux, and the properties of the flux as to melting point, surface Wetting and quality of the lead bond obtained are generally less desirable than is true of the corresponding metal bromides or chlorides. Of the ammonium halides, those preferred are the bromide and acid fluoride in admixture, and the latter can be omitted if the fiux is not required Those flux compositions which contain relatively large amounts of fluoride salts, although generally satisfactory as to fluxing properties, exhibit a tendency to give off quantities of fumes when exposed to lead burning temperatures, and this tendency may detract from their desirability.

Aqueous ammonium hydroxide is most convenient for use in preparing the composition, but the reaction may be carried out using gas-e ous or liquid ammonia with enough water to dissolve it. Throughout this specification and the appended claims, reference to reaction with ammonia will be understood to indicate reactions described herein whether they involve ammonia as such, ammonium hydroxide, or am monia supplied in another form. In any case, the amount of ammonia used is considerable less than the stoichiometric proportion required for complete formation of animine complexes with the metal halides, which are usually considered to be formed as illustrated by the equation:

The new flux may be prepared by mixing the metal halides and ammonium halides in dry powder form. This mixture is then introduced into a closed vessel provided with means for agitation of the contents. The ammonia, either as a solution of ammonium hydroxide, for example, the usual commercial product containing about 28% NHiOH, or in another form, is introduced gradually into the container with continuous agitation. An exothermic reaction takes place with the formation of a clear, mobile liquid, and the term perature reached during this reaction may be around 180 C. to 200 C. When the reactants have cooled, for example, to around 100 0., water may be added to obtain the fluidity desired in the final composition. The new flux composition thus prepared is substantially neutral, and its residues, after contact with molten lead, are so nearly neutral as to be inert, or substantially so, to all common metals. The flux compositions according to this invention have relatively sharp melting points, and are fluid at temperatures not greatly above 100 C. They are characterized by marked affinity for metal surfaces which they wet readily, and which they cause to be thoroughly wetted by molten lead to promote rapid and thorough fusion-bonding between the lead and the metal surface.

The following specific example illustrates a preferred embodiment of the flux of my invention:

Pounds Zinc chloride 60 Stannous chloride 1 2 Silver chloride 1 Ammonium bromide 3 Ammonium acid fluoride (NHiFI-IF) 1 Ammonium hydroxide (28%) 23 Water The dry ammonium and metal chlorides were mixed in a closed container equipped with an agitator. The ammonium hydroxide solution was added to the dry salts in small increments with continuous agitation. A vigorous reaction ensued and the temperature of the reactants rose to about 200 C. When all of the ammonia had been added, the contents of the autoclave formed a clear solution. Agitation was continued, and when the temperature of the product was about 120 C., the water was added. When cooled to room temperature, the composition had a pastelike consistency well adapted for application as a flux for lead burning and the like. Referring to Fig. 1 the point marked A indicates the location in the diagram of the composition of this example.

This particular composition was found to behave substantially as a unitary compound on melting and cooling as is shown by its melting" point curve reproduced as Fig. 2 of the accompanying drawing. Referring to Fig. 2, the curve shows the temperature of the flux in degrees centigrade plotted against time in minutes. This curve emphasizes the ease with which the novel flux can be applied and melted with resultant economy of time in operations using it. This flux has a pH value of 5, and its residues, after its use in lead burning, are substantially noncorrosive to metals. Another desirable characteristic of this particular flux composition is the almost total absence of fumes associated with its use in lead burning.

A flux composition as described in the foregoing example was employed in lead burning to apply a lead coating directly to the inner surfaces of a mild steel tank. The steel was cleaned only by sand blasting. It was found possible to apply lead by the aid of this flux at the rate of 25 square feet of lead coating per pound of flux used, and to apply a suflicient thickness of lead as a single coating to enable the tank to be used for the treatment of sulfuric acid. The ease with which lead burning proceeds with the new flux in comparison with previously known flux compositions is shown by the fact that in practices such as this, it has been considered heretofore that approximately 15 square feet per day of finished lead surface constituted satisfactory production by an experienced lead burner. With the new flux, production rates as high as :50 square feet per day can be attained by 'a lead burner.

The lead referred to in the operations just described was a soft lead known as Chemical Lead. Chemical Lead is a designation used in the trade to described the undesilverized lead produced from Southeastern Missouri ores, and which contains from 0.04 to 0.08 percent of copper, from 0.005 to 0.015 percent of silver and less than 0.005 percent of bismuth.

A typical analysis of Chemical Lead is:

Silver 0.00'70% Antimony 1 0.0030 Bismuth 0.0030% Copper 0.0600% Iron 0.0015% Cobalt and nickel 0.0080% Arsenic and zinc Trace Lead 99.9175% The fluxes provided by this invention bring their greatest benefits to lead burning in which substantially pure lead is joined to metal structures, but they are by no means limited to such uses, and are of positive value in working with all forms of lead and its alloys wherever a flux is or can be employed.

One advantage of my new flux is the thoroughness with which lead can be bonded to metals by its aid. To illustrate this, ultimate strengths were determined for composite sections taken from steel plates coated with Chemical Lead by lead burning employing the new flux in comparison with the parent lead metal. This lead has an ultimate strength between 2300 and 3000 pounds per square inch. In a typical example in which this lead was bonded to a sand blasted tests, and others, have shown that the flux of my invention enables bonds of exceptional strength to be obtained between lead and other metals by means of lead burning practices employing this flux.

Various modifications and adaptations of the flux herein described and in methods employing it will be apparent to those skilled in the art, and such modifications are within the scope of the invention as defined by the appended cla ms.

I claim:

1. Flux for lead burning and the like composed essentially of from about 50 to about 80 mol percent of azinc halide, together with from about 1 to about 4 mol percent of at least one of the group consisting of tin, silver, lead and gold halides reacted with ammonia in an amount equivalent to at least about one-eighth but not more than about three-tenths of that required for complete formation of ammlne complex salts with said metal halides, and containing also from about 2 to about 7 mol percent of at least one ammonium halide, said flux being substantialiy homogeneous and fluid at temperatures not greatlyabove 100 C., and characterized by af;-'

finity for and wetting of metal surfaces to promote rapid and thorough fusion bonding of lead and alloys rich in lead to said surfaces by said flux, the residues of said flu I contact with molten lead being substar corrosive to metals.

2. Flux for lead burning and the like composed essentially of from about 55 to about 20 mol percent of zinc chloride, together with from about 2 to about 3 mol percent of a mixture of stannous chloride and silver chloride, the stannous chloride predominating over the silver chloride in said mixture, said metal chlorides reacted with ammonia in an amount of at least about 20 mol percent and less than that required for complete formation of ammine complex salts with the metal chlorides and containing also from about 3 /2 to about 6 mol percent of ammonium bromide, said flux being substantially homogeneous and fluid at temperatures not greatly above 100 C., and characterized by amnity for and wetting of metal surfaces to promote rapid and thorough fusion bonding of lead and alloys rich in lead to said surfaces wetted by said flux, and by the substantial absence of fumes when exposed to lead burning temperatures, the residues of said flux after its contact with molten lead being sub stantially non-corrosive to metals.

3. Flux for lead burning and the like composed essentially of from about 55 to 70 mol percent of zinc chloride, together with from about 2 to about 3mol percent of a mixture of stannous chloride and silver chloride, the stannous chloride predominating over the silver chloride in said mixture, said metal chlorides reacted with from about 20 to about 30 mol percent of ammonia (as NI-IrOl-l) and containing also from about 3 /2 to about 6 mol percent of a mixture of ammonium bromide with a small amount of ammonium acid fluoride, said flux being substantially homogeneous and fluid at temperatures not greatly above 100 0., and characterized by affinity for and wet? ting of metal surfaces to promote rapid and thorough fusion bonding of lead and alloys rich in lead to said surfaces wetted by said flux, and the substantial absence of fumes when exposed to lead burning temperatures, the residues of said flux after its contact with molten lead being substantially non-corrosive to metals.

4. Flux capable of promoting the fusion bonding of lead directly to steel surfaces and essentially composed of Partsby weight said flux having a paste-like consistency and be ing substantially identical with that resulting from reaction of the said metallic and ammonium halides with the said ammonium hydroxide at elevated temperatures up to about 200 C., followed by addition of the said water to the reaction mixture when cooled to about 120 C.

5. Method of making flux compositions which comprises reacting a mixture composed essentially of a major proportion of one of the group consisting of halides of zinc and cadmium and a minor proportion of at least one of the group consisting of tin, silver, lead and gold halides with an ammonium hydroxide solution containing ammonia in an amount equal to from about one-eighth to about three-tenths that required for complete formation of ammine complex salts with said metal halides under conditions such that the temperature of from about 180 to about 200 C. is attained, incorporating at least one am, monium halide with the reaction product, cool: ing the composition to a temperature in the neighborhood of about 100 to 120 C., and adding water to the product to produce the degree of consistency desired in the flux. 7

6. Method of making a flux composition which comprises forming a mixture containing f om about 50 to mol percent of zinc chloride, about 1 to 11 percent of at least one of the group consisting of tin, silver, lead and gold halides, and from about 2 to about '7 mol percent of at least one ammonium halide, reacting the metal halides in said mixture with from about 20 to 30' mol percent of ammonia (as NI-IrOH) under conditions such that the reaction mixture attains a tempera, ture between about 180 and about 200 0., cooling the reaction mixture to a temperature in the neighborhood of about to C., and adding water to the product to produce the consistency desired in the flux. I

JAMES BOWDEN.

CETED The following references are of record in the of this patent:

STATES PATENTS Number Name Date 280,466 Graham -July 3, 1883 1,703,019 Spengler Feb. 19, 1929 1,960,239 Callis et al May 29, 1934 2,012,809 Derick Aug. 2'7, 1935 2,390,440 Kalil Dec. 4, 1945 

1. FLUX FOR LEAD BURNING AND THE LIKE COMPOSED ESSENTIALLY OF FROM ABOUT 50 TO ABOUT 80 MOL PERCENT OF A ZINC HALIDE, TOGETHER WITH FROM ABOUT 1 TO ABOUT 4 MOL PERCENT OF AT LEAST ONE OF THE GROUP CONSISTING OF TIN, SILVER, LEAD AND GOLD HALIDES REACTED WITH AMMONIA IN AN AMOUNT EQUIVALENT TO AT LEAST ABOUT ONE-EIGHTH BUT NOT MORE THAN ABOUT THREE-TENTHS OF THAT REQUIRED FOR COMPLETE FORMATION FO AMMINE COMPLEX SALTS WITH SAID METAL HALIDES, AND CONTAINING ALSO FROM ABOUT 2 TO ABOUT 7 MOL PERCENT OF AT LEAST ONE AMMONIUM HALIDE, SAID FLUX BEING SUBSTANTIALLY HOMOGENEOUS AND FLUID AT TEMPERATURES NOT GREATLY ABOVE 100* C., AND CHARACTERIZED BY AFFINITY FOR AND WETTING OF METAL SURFACES TO PROMOTE RAPID AND THOROUGH FUSION BONDING OF LEAD AND ALLOYS RICH IN LEAD TO SAID SURFACES WETTED BY SAID FLUX, THE RESIDUES OF SAID FLUX AFTER ITS CONTACT WITH MOLTEN LEAD BEING SUBSTANTIALLY NONCORROSIVE TO METALS. 